One conventional method of cooling water for the purpose of heat exchange is to circulate the heated water downwardly through a cooling tower that separates the water into droplets, thus dramatically increasing its exposed surface area. Simultaneously air is circulated through the various trays of the cooling tower to enhance its heat exchange characteristics. Although water cooling towers of this general nature have been in wide use for many years and have been powered by systems of varying nature, including mechanical drive systems, electrical drive systems, hydraulic energization, etc., most recently it has been the practice to provide water cooling tower systems with electrically energized drive systems for fan operation. In such cases, the cooling air is moved by a rotating fan turned by a fan deck mounted speed-reducing gear box connected to an electric motor by a shaft and flexible couplings. The electric motor, shaft and flexible couplings generally are mounted on the fan deck of the water tower which is itself mounted at a substantial height above the ground level. While such systems function adequately, they nevertheless have significant disadvantages from the standpoint of operation, safety, efficiency, etc.
The electric motor, shaft and coupling assembly, together with the fan mechanism are quite heavy and therefore place significant weight at the upper portion of the water cooling tower. This of course requires the structure of the cooling tower to be capable of supporting this significant weight, which typically adds to the cost to the cooling tower structure itself. It is desirable to provide a cooling tower fan assembly having minimal weight characteristics to thereby more efficiently provide for its support in the upper portion of a cooling tower without necessitating that the cooling tower be designed to support a heavy cooling fan system.
Because cooling tower fan assemblies in use at the present time are typically powered by electric motors, these motors and other electrically equipment associated therewith constitute an electrical hazard and a fire hazard that can subject personnel and equipment to a certain degree of danger. Maintenance activities for these types of motor driven fan assemblies require service personnel to gain access to the fan deck in the upper portion of the cooling tower. Obviously the fan deck can become slippery due to build up of deposits that result from circulation of water or other cooling tower fluid through the cooling tower system. Maintenance workers can therefore be subject to injury by falling because of these slippery surfaces. Further, since the electric motor is operative in a "wet" environment, being physically located in the upper portion of the cooling tower, it can subject maintenance workers to electrical hazards when maintenance activities are being conducted about the motor or fan assembly. Further, degradation of the electrical motor during its service life can result in the creation of a fire hazard for the cooling tower structure. Since cooling towers typically incorporate wood in a significant portion of the structure thereof, although the wood is typically liquid soaked and not easily ignited, nevertheless a deteriorated electrical motor and its electrical components can develop a fire hazard due to electrical arcing. Such fire hazards are especially dangerous to workers that might be present at the mechanical deck of the cooling tower should electrical arcing develop.
As mentioned above, the fan assembly of a typical cooling tower incorporates a speed-reducing gear box that is connected in driven relation to an electric motor and in driving relation to a shaft and flexible couplings. These mechanical structures, being operative in the "wet" environment of the cooling tower and being more or less continuously operated, will deteriorate after a period of time and require replacement. Replacement operations for such mechanical devices as the speed reducing gear box or the electric motor will require significant effort on the part of maintenance personnel and significant down time of the cooling tower system simply due to the necessity of conducting these operations at the fan deck elevation of the cooling tower. Moreover, special lifting equipment may be required as well. It is desirable, therefore, to provide a cooling tower system having a fan assembly that is capable of simple and quick maintenance or replacement should such servicing activities, be required.
When operable in a warm climate most cooling tower systems are not subject to freezing. However cooling towers that are located in cooler climates frequently require considerable maintenance to prevent freezing during cold weather conditions. Further, the tendency of freezing is enhanced because for the most part, the fan systems of the cooling towers are limited to unidirectional rotation. Such cooling towers must ordinarily be provided with an anti-freeze additive to prevent freezing of the cooling tower fluid. This of course increases to the cost of operation of the cooling tower and thus results in a commercial disadvantage for the commercial system incorporating the cooling tower. It is desirable to provide a cooling tower system that is capable of being efficiently controlled in a manner that will significantly reduce the likelihood of freezing during cold weather conditions.
Most cooling tower systems having electric motors, gear box and shaft drive mechanisms such as that set forth above, typically incorporate a unidirectional drive system that is capable of operation only at a designed fan drive speed. Obviously when the cooling tower fan system is only capable of single speed operation, its speed must be characterized according to the maximum heat transfer conditions that can be expected at any given point in time. For this reason, cooling tower fan systems are not ordinarily energy efficient. Typically, the electric motor and fan drive systems of most cooling tower mechanism are engineered to produce 100% CFM of peak air on demand. Therefore, in climates having only two or three months of elevated temperatures during the year, while the rest of the year is significantly cooler, there is typically a substantial over use of energy with a constant peak RPM fan drive system which thus over produces cooling air and wastes energy. It is desirable therefore to provide a cooling tower fan drive system that has the capability of efficiently operating at speeds that are selected responsive to the heat exchange requirements that exist in any given point of time. It is desirable to provide a cooling tower fan system incorporating a controller to automatically adjust the speed of the fan and hence the cooling system to process requirements determined by ambient temperatures of the environment.
When cooling towers are subjected to hazardous weather conditions such as tornados, hurricains etc. high velocity wind conditions can cause severe damage to the large, relatively light weight fan structures that are typically provided in most cooling towers. Where there is sufficient advance warning of such hazardous weather conditions it is typically appropriate for maintenance personnel to enter the water tower, climb to the elevation of the fan system and physically secure the fan against rotation by tieing it to the water tower structure by means of ropes or other such devices. After the adverse weather condition has dissipated it is then necessary for maintenance personnel to again climb into the tower to release the fan for normal operation. These activities require labor and therefore expense that might be avoided. Also, such activities subject maintenance personnel to a certain degree of danger especially if the fans are being secured during turbulent, windy conditions. It is also desirable therefore to provide a novel cooling tower fan system wherein the fan may be effectively secured against rotation without necessitating entry of the water tower system by maintenance personnel to either secure or release the fan.